Leaders of Washington's homosexual community and several City Council members gathered outside the Marine Barracks on Capital Hill yesterday to protest last Saturday's assault on the owner of a gay bar by a group of apparently drunken Marines.

The 30 gay activists announced the formation of GEMS -- Gay Ex-Marines -- a group that they said would try to sensitize the U.S. Marine Corps not only to the needs of what they estimated as at least 19,000 homosexuasls within its ranks but also to the gay community in general.

Denouncing last Saturday's assault at the Equus Bar, Gay Activists Alliance president Melvin Boozer said, "there exists within the walls of the Marine Corps barracks an atmosphere which is conducive to the premeditation and formulation of collective acts of violence by Marine personnel against . . . gay men."

Boozer said the alliance would use whatever influence and resources it has "to insure . . . that the streets are made safe for gay and lesbian citizens." He called upon barracks commandant Col. J.P. Monahan to act within two weeks to:

Identify the Marines involved in the incident, tell what punishment they would be given, and what steps will be taken to prevent "further victimization" of gays by Marines.

Pay for damage done to the bar and apologize to its owners.

Work with the gay community to "generate mutual respect between Marines and gays."

A spokesman for the commandant refused to comment yesterday on the incident or on Boozer's demands.

Marie Dias, Mayor Marion Barry's liaison to the gay community, said, "The mayor's office feels that a violent attack of this nature . . . cannot be tolerated. We will follow the Marine investigation and make sure those who participated will get their day in court, so to speak."

The press conference came after an incident last Saturday in which a group of Marines -- first said to number two dozen but now believed to be only five -- went into the bar at 639 Pennsylvania Ave. SE, brandishing sticks and shouting antihomosexual slogans. Several of the bar's windows were smashed and one of its owners was assaulted.

The incident occurred around midnight, when the Marines broke away from a rowdy group of about 150 persons that had gathered in a small park across from the bar. Two Marines were later arrested, charged with disorderly conduct and released to military authorities after paying fines of $10 each.

Boozer said at the press conference that Saturday's incident was the sixth time since April that the owners and patrons of the gay bar Equus "have been subjected to harassment, taunting and violence by an anonymous mob hiding behind uniforms of America's military elite."

The city's estimated 70,000 gays have enjoyed relatively hassle-free movements in Washington, due to the District's strong human rights laws.

However, tensions between gays and Marines have been simmering for some time. Owners of gay bars and restaurants in the Capitol Hill area have said they have had trouble with Marines harassing their patrons for some time, and several gays have been assaulted by Marines at the Iwo Jima Memorial in Arlington, which has become a late-night meeting place for some area homosexuals. Some Marines also say they have been assaulted by gays.

Several City Council members, including the Rev. Jerry A. Moore Jr. (R-At Large), John Ray (D-At Large), Nadine P. Winters (D-Ward 6) and John A. Wilson (D-Ward 2), and two council hopefuls from Ward 7, Democrats H. R. Crawford and Emily Y. Washington, also voiced their distress at the Marine action. They called for a full investigation of the incident.

Nick Makalary, a former Marine intelligence sergeant, acted as a spokesman for GEMS, the newly-formed gay group. "We in GEMS will remain highly visible, insuring that the public also knows of the loyal service of its Gay Marines," Makalary said.